Heat treatment of membranes of selected polyimides,polyesters and polyamides

ABSTRACT

CERTAIN POLYMERIC MEMBRANES ARE HEATED AT ELEVATED TEMPERATURES TO IMPROVE THEIR GAS SEPARATION ABILITIES.

Y 3974 H. H. HOEHN HEAT TREATMENT OF MEMBRANES OF SELECTED POLYIMIDES, POLYESTERS AND POLYAMIDBS Filed NOV. 2. 1972 United States Patent Ofitice 3,822,202 Patented July 2, 1974 3,822,202 HEAT TREATMENT OF MEMBRANES F SELECTED POLYIMIDES, POLYESTERS AND POLYAMlDES Harvey Herbert Hoehn, Hockessiu, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del. Filed Nov. 2, 1972, Ser. No. 303,210 Int. Cl. BOld 13/00 US. Cl. 21023 32 Claims ABSTRACT OF THE DISCLOSURE Certain polymeric membranes are heated at elevated temperatures to improve their gas separation abilities.

BACKGROUND OF THE INVENTION Field of the Invention This invention concerns a method of improving the utility of selected polymers as gas separation membraues.

Prior Art Polymeric materials useful as semipermeable membranes are known. U.S. Pats. 3,172,741 issued to Jolley and 3,567,623 issued to Richter and Hoehn disclose semipermeable membranes made from various polymers.

Copending application of Hoehn and Richter Ser. No. 273,802, filed July 20, 1972, now abandoned, discolses a selected group of polyimides, polyesters and polyamides which are useful as gas separation membranes because of their molecular morphology. These are aromatic polyimides, polyesters and polyamides in which the repeating unit of the main polymer chain (a) has at least one rigid divalent subunit, the two main chain single bonds extending from which are not colinear,

(b) is sterically unable to rotate 360 around at least one of the bonds noted in (a), and

(c) has 50% or more of the atoms in the main chain of the repeating unit of the polymer as members of aromatic rings.

None of the above art discloses improvement of gas separation properties as a result of heat treatment.

DESCRIPTION OF THE INVENTION There has now been discovered a process for preparing improved gas separation membranes by (1) dissolving in a suitable organic solvent a polyimide, polyester or polyamide in which the repeating unit of the main polymer chain is characterized by (a), (b) and (c) above; (2) forming a membrane from this solution by casting or extruding it into a film or spinning it into a hollow tube or fiber; (3) removing sufficient solvent by evaporation and/or by solvent extraction to render the membrane self-supporting; and (4) heat treating the resulting membrane at a temperature in the range of about 150 C. up to just below the temperature at which the mechanical integrity, strength and other physical properties of the polymeric membrane are significantly impaired. Generally speaking the highest temperature used should be just below the softening point of the polymer. For practical purposes the range of ISO-340 C. can be used. Preferred is the range of 200340 C.

The membranes obtained in step (3) may be further air-dried or vacuum-dried at room temperature or at a temperature below 150 C. prior to the heat treatment of step (4).

The time of heat treatment may be varied widely. The only essential is that the heating be long enough to bring the membrane to the desired heat treatment temperature. When very thin membranes are heat-treated by efficient means, e.g., by infrared heating, substantial improvement in membrane properties may be obtained within one second. Further improvement may be obtained by continuing the heat treatment up to six hours or more. There is no significant advantage in continuing the heat treatment beyond 24 hours. The improvement takes place while the membrane is at a temperature above C. and is not alfected by the rate or manner of cooling after the heat treatment. Care should be taken that the combination of time and temperature used do not significantly impair the mechanical integrity, strength, or other physical properties of the polymer.

The heat treating process may be carried out in air, in an inert gas such as nitrogen or helium, or under vaccum. Where the heat treatment is to be continued for more than a few seconds, or is to be conducted at high temperatures, e.g., above 350 C., it may be preferable to conduct the heat treatment in an inert gas or under a vacuum to avoid oxidative degradation of the membrane, although this is not essential.

As illustrated in the examples which follow, the heat treatment step of the present invention produces a substantial increase in the selectivity with which the treated membranes separate gases having diiferent molecular weights and/or molecular sizes. With some of the polymers the improved selectivity obtained by heat treatment is also accompanied by an increase in the overall flow rate of small gas molecules, e.g., hydrogen. With other polymers, the flow rates may be somewhat reduced by heat treatment, although the molecular morphology of the selected polymers ensures that a practical flow rate will be retained.

The polymers for use as membranes in the process of this invention are selected because of the inability of their molecules to pack densely as discussed below. While it is desired not to be bound by theory, it may be postulated that the improvements efl'ected by the heat treatment are the result of increased uniformity of packing of the polymer molecules. This results in a network of molecules having a free volume favorable to high transport of small gas molecules such as hydrogen but unfavorable to transport of larger molecules such as methane, higher hydrocarbons, C0, C0 S0 and the like. Because of their molecular morphology, the unheated polymers are capable of only a certain degree of closeness of packing in the membrane. However, this degree of closeness is not uniformly achieved in ordinary casting or spinning processes. Heating above 150 C. appears to relax the polymer chains so that more of the chains achieve their maximum closeness of packing and thereby a maximum uniformity of packing and free volume. Such increased uniformity of structure may account for the improved gas separation properties observed.

Heat treatment as in the present invention would be deleterious to membranes of polymers of some known types other than those employed herein. It is known that membranes of such materials as cellulose esters, vinyl-type polymers, and even ordinary polyimides, polyesters and polyamides tend to have their molecules closely packed when they are formed into membranes. Heat treatment of such membranes serves only to reduce their permeability.

The present invention is a method for improving a gas separation membrane of which at least 50% by weight consists essentially of a polymer whose main chain has a repeating unit containing at least one group selected from the group aromatic imide, aromatic ester and aromatic amide in which said repeating unit (a) contains at least one rigid divalent subunit, the two main chain single bonds extending from which are not colinear,

(b) is sterically unable to rotate 360 around one or more of said main chain single bonds, and

(c) has at least 50% of the atoms in the main chain as members of aromatic rings.

These criteria define predominantly aromatic polymers whose molecules are unable to pack densely because of having within the repeating unit of the polymer chain at least one main chain single bond which makes an angle with at least one next adjacent main chain single bond and around which the polymer molecule is sterically unable to rotate freely. While it is not intended to be bound by speculation, it is considered that configurations as defined above render such polymer molecules incapable of packing as densely together as polymer molecules without such configurations. Specifically, the bend in the polymer chain caused by the noted angle cannot be accommodated in packing by free rotation around the bond. The structure of the solid polymer is thus kept permanently more open to the passage of small gas molecules, resulting in higher flux rates for the passage of such gases.

The polyimides from which membrane materials of this invention are selected may be represented generally as polymers in which the repeating unit is as shown in formula I:

Twists} wherein R and R alike or different, are divalent organic radicals, i.e., with their bonds stemming from carbon atoms. These are also illustrated in more detail below.

The polyamides from which the membrane materials of this invention are selected may be represented generally as polymers in which the repeating unit is as shown in formula III:

wherein R and R are defined as above and R is hydrogen, lower alkyl, or phenyl. These are illustrated in more detail below. The term lower in the specification and claims means l-6 carbons.

The particular polyimides, polyesters and polyamides useful as membranes in this invention are selected on the basis of the three criteria noted above. Requirement (a) specifies that the repeating unit of the polymer contain at least one rigid divalent subunit, the two main chain bonds from which are not colinear. The rigid subunits in a polymer chain are those atoms, groups of atoms, or cyclic structures which are joined to other units in the main chain by single bonds between two atoms. The single bond junction points in a polymer main chain are readily recognized from the structural formula of the polymer repeating unit and these points are the demarkation points between rigid subunits. Such a subunit is rigid because the angle between the two single bonds extending from the subunit is fixed. The two bonds from a rigid subunit are colinear (L) if they form an angle of about 180 (particularly -180") or if they are parallel and offset not more than 2 A. Otherwise, they are noncolinear (N). Preferred polymers have 2-10 mainchain rigid subunits in the polymer repeating unit.

Requirement (b) specifies that the polymer chain con tain at least one bond between rigid subunits around which bond the polymer chain is sterically prevented from rotating 360. This determination is based on the wellknown textbook rules of stereochemistry. These rules are strictly incorporated into the design of the Corey-Pauling- Koltun Models (CPK Models) described by W. L. Koltun in Biopolymers, 3, 665-79 (1965) and which are available from the Ealing Corporation, 2225 Massachusetts Ave., Cambridge, Mass. 02140.

A practical determination of whether a polymer satisfies requirements (a) and (b) is made as follows:

(1) Draw the conventional two-dimensional representation of the polymer repeating unit and indicate the single bonds in the main polymer chain which separate rigid subunits.

(2) For each rigid subunit indicate whether the two main chain bonds stemming from it are colinear (L) or noncolinear (N).

(3) Construct the CPK Model of the polymer unit and from the model determine which of the bonds indicated in (1) are restricted from rotating through 360. Persons skilled in the field of stereochemistry would, of course, not need the model to make this determination. Illustrations of the above steps and the one which follow appear in the examples below.

The determination of requirement (c) that at least 50% of the atoms forming the backbone chain of the repeating unit of the polymer be in aromatic groups can readily be made from the two-dimensional representation of the polymer repeating unit noted above. The main chain atoms which are counted are those in the single atom and cyclic rigid subunits. In cyclic subunits in which the two single bonds stem from different atoms, all member atoms in the basic ring of the subunit are counted, e.g., p-phenylene counts 6 atoms. Side chain atoms such as hydrogen, carbonyl oxygen, alkyl groups, haloalkyl groups, carboxyl groups, ester groups, halogen substituents and other pendant groups are not counted. If both single bonds from a cyclic "rigid subunit stem from the same atom, only that one atom is counted, e.g., 1,1-cyclohexylene counts 1 atom, the remaining pentamethylene being a pendant group. Aromatic rings include not only the hydrocarbon aromatic rings such as benzene, naphthalene, anthracene, penanthrene, pyrene, chrysene, naphthacene, indene, and the like, but also those heterocyclic rings commonly acknowledged to have aromatic character such as furan, benzofuran, thiophene, pyrazole, indole, benzimidazole, pyrazine, carbazole, pyridine, quinoline, acridine, imidazole, isoimidazole, and the like. See, for example, R. C. Fuson, Advanced Organic Chemistry, John Wiley & Sons, Inc., New York, N.Y., 1950, Chap. XXIV, Aromatic Character.

In the examples showing the determination of the above criteria, the single bonds separating rigid subunits are marked by drawing dotted lines across the two-dimensional representation of the polymer repeating unit and are identified by the letters A, B, C, D, etc. The rigid subunits are numbered 1, 2, 3, 4, etc. The rigid subunits are then tabulated along with a notation for each whether its two main chain single bonds are colinear (L) or noncolinear (N) and a notation as to which, if any, of these bonds are restricted from rotating 360. The proportion of the main chain atoms in the repeating unit which are in aromatic structures is also shown.

The invention also contemplates the use of copolyimides, copolyesters and copolyamides in which the respective repeating units of the copolymer members individually satisfy criteria (a), (b), and (c), as well as physical blends of two or more of these materials meeting these criteria and also copolyimides, copolyesters, copolyamides and blends in which one or more members meet these criteria, those members constituting 50% or more of the membrane by weight.

In a preferred embodiment of this invention, a polymer which satisfies requirements (a), (b) and (c) is dissolved at about 20% concentration in an anhydrous organic solvent. The solution is filtered to remove solids and is freed of dissolve gases. At a temperature in the range from room temperature up to 150 C., the solution is cast in film form onto a support or spun through a cored spinneret to give a hollow fiber. The solvent is then removed. For example, if a uniform membrane is desired, the solvent is evaporated preferably by heating at about 90- 1l0 C. On the other hand, if an asymmetric membrane is desired, the film or fiber structure is quenched in a liquid which is a nonsolvent for the polymer and a solvent for the organic solvent already present. Preferably the quench liquid is water and the organic solvent is watermiscible. The membrane is then heat-treated by bringing it to a temperature in the range from l50500 C.

Apparatus suitable for separation of gases, as removal of hydrogen from a mixture of hydrogen and methane, by a membrane in film form is shown in the Figure. In this Figure base section 11 and upper section 12 of permeation cell are machined from corrosion-resistant metal. Film 13, the separation membrane, is in the form of a disk mounted against a porous support disk 14. When upper section 12 of the cell is bolted to lower section 11, synthetic elastomer O-rings 15 seat firmly around the periphery of the membrane and against the metal. Inlet 16 for feeding gases into the cell is near the membrane. Bypass of a portion of the feed gas is provided through exit 17. Gas passed through membrane 13 is collected through a metal frit 18 into exit pipe 19. Pipe 19 is connected to a metal gas receiver (not shown) which is fitted with pressure measuring devices.

Some of the terms used to describe the performance of the membranes of this invention are defined as follows:

Selectivity The selectivity of a membrane in separating a two-component fluid mixture is defined as the ratio of the rate of passage of the more readily passed component to the rate of passage of the less readily passed component. Selectivity may be obtained directly by contacting a membrane with a known mixture of gases and analyzing the permeate. Alternativley, a first approximation of the selectivity is obtained by setting up the ratio of the rates of passage of the two components determined separately on the same membrane. Rates of passage may be expressed in GTR or cB units. Thus S =200 indicates that the membrane in question allows hydrogen gas to pass through at a rate 200 times that of methane.

Gas Transmission Rate (GTR) One characterization of membrane permeability used in this disclosure is the gas transmission rate. GTR data represent the steady state rate of gas transmission through a membrane. GTR values are not normalized for membrane thickness. For homogeneous membranes the GTR is inversely proportional to the sample thickness. When the thickness of the active part of the membrane is not known, e.g., in asymmetric membranes, the GTR is still a valid permeability characterization. GTR values deter mine the value-in-use of the membrane in a permeation device. Derivation of the GTR equation follows.

6 The volume of gas transmitted through a membrane is directly proportional to the area, time, and pressure of the permeation test as shown in (1).

volume are-.1 time X pressure GTR:

usually measured at gas pressures of 39.7, 114.7, 314.7, 614.7, and l0l4.7 p.s.i.a.

Centibarrer Permeation Coefficient (cB) The standard unit for the permeability coefficient in observing me permeability of polymer films to gases is defined as the barrer which is equal to:

10 cm. (STP) cm. cmFXseeXcm. Hg

GTR:

in which cm. (STP) is the volume of permeated gas at standard temperature and pressure,

cm. is the thickness of the film,

cm. is the area of film,

sec. is the time, and

cm. Hg is the pressure.

(ASTM Test D1434-66, 1970 ed., Part 27, pages 447 and 453).

In the present application, permeabilities are reported in centribarrers (cB), a unit which is of the barrier as defined above. Centibarrer values can be calculated from the relationship:

cB=GT RX film thickness in mils 0.6.

As stated previously, the polymers used in this invention are characterized by having the three elements (a), (b) and (c). As long as these are present in the polymer, R, R and R may be any divalent organic radical and R may be any tretravalent organic radical. It is to be noted that it is possible to prepare polymers where all the Rs are derived from compounds shown in the various tables below but would still not have elements (a), (b) and (0). Such polymeric materials are not within the scope of the invention, but may be used in combination with the polymers of this invention in amounts up to 50% by weight.

The examples give various illustrations of the radicals which are used. Without any intent of limitation, the radicals may be further illustrated as follows:

In formulas I, II and III, the divalent radicals R, R and R may be substituted or unsubstituted phenylene, naphthylene, biphenylene, anthrylene, or

where R is alkylene (including alkylidene) of up to 18 carbon atoms, aralkylene of up to 18 carbon atoms, haloalkylene (including haloalkylidene) of up to 18 carbon atoms in which the halogen(s) are fluorine, chlorine, bromine or iodine, oxygen, sulfur,

in which R and R are lower alkyl or phenyl. Preferred embodiments of R are alkylidene, haloalkylidene, aralkylidene, oxy and iminocarbonyl (--NH-CO). Preferred alkylene and haloalkylene moieties in R are those of 1-3 carbon atoms.

The tetravalent radical R may be a substituted or unsubstituted grouping:

where R is defined as above.

Substituents on the above divalent and tetravalent radicals, i.e., replacements for hydrogen in aromatic C-H groups, may be alkyl of up to 18 carbon atoms such as methyl, ethyl, isopropyl, butyl, tert-butyl, hexyl, and octadecyl, phenyl, halogen such as fluorine, chlorine, bromine and iodine, lower alkoxy, carboxyl, lower alkoxycarbonyl, carbacyl of up to 6 carbon atoms such as aoetyl and hexanoyl, sulfo and sulfo salt of an alkali or alkaline earth metal. Preferred embodiments of R, R R and R are those in which the aromatic portions are the benzene or naphthalene series.

Additional dianh'ydride radicals are listed in Table I. Suitable polyirnides for use in this invention can be obtained when equivalent amounts of the dianhydrides shown in Table I are substituted, e.g., for 3,4,3,4-diphenylhexafluoroisopropylidene tetracarboxylic dianhydride in the procedure of Example 4, Part A.

Additional diamines are listed in Table II. Suitable polyimides can be obtained when equivalent amounts of the diamines shown in Table II are substituted, e.g., for 1,5-diaminonaphthalene in the procedure of Example 10,

Part A.

Polyesters suitable for use in this invention are obtained when, as in the procedure of Example 21, Part A, 4,4 diphenylbis(trifluoromethyl)methane dicarboxylic acid dichloride is substituted, e.g., for isophthaloyl chloride and the diols shown in Table III are substituted, e.g.,

for 2,2-bis 3,5-dichloro-4-hydroxyphenyl) propane.

Additional suitable polyesters are obtained when equivalent amounts of the diacid chlorides of the dicarboxylic acids shown in Table IV are substituted, e.g., for isophthaloyl chloride in the procedure of Example 21,

Part A.

Additional suitable polyamides are obtained when equivalent amounts of the diacid chlorides of the dicarboxylic acids shown in Table -IV are substituted for isophthaloyl chloride in the procedure of Example 22, Part A, or when diphenylbis(trifluoromethyl)methane-4,4-dicarboxylic acid dichloride is substituted for isophthaloyl chloride and equivalent amounts of the diamines shown in Table II are substituted for 4-isopropylmetaphenylenediamine in the procedure of Example 22, Part. A.

A preferred group of polyesters and polyamides are copolyesters and copolyamides formed by reacting a glycol or a diamine with an equivalent amount of a mixture of isophthaloyl and terephthaloyl chlorides where the molar and weight proportions of the acid chlorides may vary from 99/1 to 1/99, respectively. Particularly preferred are copolyesters and copolyamides in which isophthaloyl chloride is used in excess of terephthaloyl chloride, especially where the ratio is 70/30.

TABLE I Dianhydrides 1 Pyrornellitic diauhydride.

3.4.3 ,4-diphenylsulionetetra- 12. 1, 4, 5, &naphthalenetetracarcarboxylic dianhydride.

methnnetetracarboxyllc a: dianhydride.

6- 3. 4. 3, 4-di phenyldl (trlflnoro C F;

methyl) methanetetracar- (5 boxylle dlanhydrlde.

7...-- 2,3. 6, 7-naphthalenetetracarboxyllc dlanhydrlde.

3. 3, 4. 3, 4'-diphenyltetracarboxylic dlanhydride.

9.. 3, 4, 9, m-perylenetetracarboxylic dianhydnde.

10- 3, 4. 3', 4-dlphenylethertetracarboxylic dianhydride. O

11.... I, 2, 4, S-naphthalenetetracar- I boxylie dianhydnde.

boxylic dianhydride.

15 16 TABLE 11IC011tfimed in 350 ml. of dry pyridine under nitrogen at 50 C. was (36) Bis(3,5-diisopropy1-4-hydroxyphenyl)sulfone added 88.87 g. of 3,4,3',4'-diphenylhexafiuoroisopropyl- (37) 1,4-Dihydroxy-2,3-dichlorobenzene idene tetracarboxylic dianhydride. The temperature rose (38) 1,4-Dihydroxy-2-bromo-3-propylbenzene to a peak of 74 C. within a few minutes. After 1 hour of 3- (P- y yp y )P stirring, 82 g. of acetic anhydride was added. The tem- 5 3- y y y p Y perature rose to a peak of 66 C. within a few minutes.

P p Stirring was continued for 3 hours, during the latter por- (41) 22'B!S(4'hydrXyPhcny1)'3'cyclohexylpropane tion of which the solution was heated to 100 C. After ggggggj ggii w fi' fi 1) cooling the solution to room temperature, the polyimide y Xy y roxyp any propane was precipitated by drowning in a large excess of methanol 4 E; 2 lii;(g ihirfyli hg di sghieiifi gz g under vigorous agitation, recovered by filtration, washed (45) 1,1 Bis(4 hydrOXypheny1) 5 pheny1pemane with methanol and dried under vacuum, first for 4 hours 47 BiS(2 hydroxypheny1)mcthane at 170 C. and then for 3 hours at 260 C. (48) 2,2'-Dihydroxy-3,5,6-trichlorodiphenylmethane 15 The p s/ p p as shown above was checked .(49) 2,2-Bis(4hydroxyphenyl)-1,3-diphenylpropane against requirements (a), (b) and (c) as follows:

4. B o D E F A Restricted Rigid subunit Collnearlty bonds L N L N E N E, F N F (50) 2,2-Bis(3,5-dichloro-4-hydroxyphenyl) The repeating unit has 4 N and 2 L subunits, 2 bonds hexafiuoropropane with restricted rotation, 3 of the N subunits have at least Preferred diols are items 1-3 540 19 24 2s 31 and mm with restricted mam, 24/32 the in chain are aromatic. 50 of Table III. Part B TABLE IV Dicarboxylic Acids A solution of 30 g. of the polyimide of Part A and p y ether 4 4, dicarboxyfic acid 170 g. of dichloromethane was filtered through a 0.45n

silver membrane, degassed and two films were cast on an Inconel sheet coated with a low molecular weight polytetrafluoroethylene wax dispersion (Vydax) at room tem- (2) Diphenyl sulfone 4,4'-dicarboxylic acid (3) Diphenylbis(trifluoromethyl) methane-4,4-

dicarboxylic acid perature in a dust-free cabinet with a 15-mil doctor knife. gf The films were dried for 15 minutes and then stripped. One

ephthalic acid film d d d 1 Th m (6) 4,4, pmpylidenedibenzoic acid was alrre an use as a contro e 0 er filfl: (7) 4Methylisophthanc acid was placed in a vacuum chamber and heat-treated at 260 (8) 4,4'-Methylenedibenzoic a id C. for 6 hours under a vacuum of 2 microns. The con- 9 pi h lfid 4,4' i 1 id trol film, 1.42 mils thick, permeated H at 3197 GTR and (10) 2,6-Pyridinedicarboxylic acid 2724 CB and 4 at 106 GTR and 90 The Hz/CH4 (11) 4,4-Diethylsilanedibenzoic acid Was 30. The heat-treated film, 1.97 mils thick, permeated (l2) 4,4'-Diphenylsilanedibenzoic acid H3 at 2907 GTR and 3436 0B and CH at 14 GTR and (13) 4,4-Bisbenzoic acid 17 0B. The Sag/CH4 was 208. The heat treatment produced acid almost a seven-fold increase in the selectivity of the mem- Bis yp y y p oxide brane with reference to hydrogen and methane. (16) 1,S-Naphthalenedicarboxylic acid (17) 4,4'-Bis(o-toluic) acid EXAMPLE 2 (18) 4-Bromoisophthalic acid A 1 b 15 207 4 f h I so ution containing 9. out to 0 o t e po yi i ands are ltgms 13 and 16 imide of Example 1, Part A, in dimethylacetamide was used to cast a series of films on Vydax coated glass SPECIFIC EMBODIMENTS OF THE at 100 C. using a 25-mil doctor knife. The films were INVENTION covered and dried for 5 minutes at 100 C. Vents in the In the illustrative examples which follow, parts and cover were then opened and the films were further dried percentages are by weight unless otherwise specified. for 10 minutes at 100 C. The films were then stripped EXAMPLE 1 from the plate. A control film was air-dried at room temperature while the remaining other films were heat- Part from 4 ll' p 9- treated for 6 hours under a vacuum of 2,2 at the respective propyliqiene tetracarboxyhc dlanhydnde and 414cm" temperatures shown in Table V. All films were then ammodlphenyl ether tested for permeation of hydrogen and methane with the To a. solution of 40.05 g. of 4,4-diaminodiphenyl ether results shown in Table V.

TABLE V Post treatment H2 perme- CH4 permetemperation ation Selecature tivity, Thickness (mils) C.) GTR cB GTR B Hr/CH EXAMPLE 3 A solution of 20 g. of the polyimide of Example 1, Part A, in 80 g. of dimethylacetamide was filtered through a 0.8 1. silver membrane, degassed, and two films were cast on a Vydax coated glass plate at 100 C. with a 25-mil doctor knife. The films were covered, dried at 100 C. for minutes, after which the vents on the cover were opened and drying continued for minutes. The films were then stripped from the plate. One film was air-dried and used as a control while the other was heat-treated under a 2,11 vacuum for 6 hours at 260 C. The control film, 2.60 mils thick, permeated H at 1378 GTR and 2150 cB and CH at 47 GTR and 73 cB. The 5 was 29. The heat-treated film, 2.62 mils thick, permeated H at 2286 GTR and 3594 0B and CH at 14 GTR and 22 cB. The Sag/cm was 163.

EXAMPLE 4 Part A.-Polyimide from 3,4,3,4'-diphenylhexafluoroisopropylidene tetracarboxylic dianhydride and 4-isopropyl-1,3-diaminobenzene To a solution of 31.21 g. of 4-isopropyl-1,3-diamin0- benzene in 350 m1. of dry pyridine under nitrogen at 50 C. was added with stirring 92.29 g. of 3,4,3',4'-diphenylhexafiuoroisopropylidene tetracarboxylic dianhy dride, rinsed in with an added 50 ml. of pyridine. Within a few minutes the temperature rose to a peak of 76 C. After stirring for about two hours, the temperature was 52 C. and 85.2 g. of acetic anhydride was added. Within a few minutes the temperature rose to a peak of 66 C. After 1 hour of stirring, the solution was heated to 99 C. and stirred for about 20 minutes. The polyimide was precipitated from the cooled solution by drowning it in a large excess of methanol under vigorous agitation. The polyimide was recovered by filtration, washed three times with methanol and dried under vacuum, first for 4 hours at 100 C. and then for 4 hours at 260 C.

The polyimide prepared as shown above was checked against requirements (a), (b) and (c) as follows:

The repeating unit has 4 N subunits, 3 restricted bonds, all of the N subunits have at least one bond with restricted rotation, 18/25 of the chain atoms are aromatic.

Part B A solution of 42.5 g. of the polyimide of Part A in 170 g. of dimethylacetamide was filtered through a 0.45 1 silver membrane, degassed and two films were cast on a Vydax coated glass plate at C. using a l5-mil doctor knife. The films were then covered and allowed to dry for 5 minutes, after which the vents in the cover were opened and films allowed to dry another 10 minutes. The films were stripped from the plate. One film was air-dried for use as a control. Another film was placed in a vacuum chamber and heat-treated at 260 C. under a vacuum of 2,1. for 6 hours. The 1.79-mil thick control film permeated H at 11,150 GTR and 11,975 cB and CH at 851 GTR and 914 cB. The SHzmH4 was 13. The 2.0l-mil thick heat-treated film permeated H at 11,407 GTR and 13,757 cB and CH at GTR and 157 cB. The SHZ/Cm was 88.

EXAMPLE 5 Part A.-Polyimide from 3,4,3',4'-diphenylhexafiuoroisopropylidene tetracarboxylic dianhydride and metaphenylenediamine To a solution of 10.81 g. of metaphenylenediamine in ml. of dry N,N-dimethylacetamide under nitrogen at 50 C. was added with stirring 44.43 g. of 3,4,3,4- diphenylhexafluoroisopropylidene tetracarboxylic dianhydride, rinsed in with an added 25 ml. of dimethylacetamide. Within 2 minutes the temperature rose to a peak of 66 C. Stirring was continued for more than an hour. With the solution at 45 C. a mixture of 82 g. of triethylamine and -82 g. of acetic anhydride was stirred in. Within 10 minutes the temperature rose to a peak of 52 C. and then began to drop. Stirring was continued for about 2 hours. The resulting polyimide solution in dimethylacetamide was concentrated to 32% by evaporation, diluted to 10% by adding 359 g. additional dimethylacetamide and then concentrated to about 15% polyimide by evaporation and used without further treatment.

The polyimide prepared as shown above was checked against requirements (a), (b) and (c) as follows:

Repeating unit has 4N subunits, 2 bonds with restricted rotation, 3 of the N subunits have at least 1 bond with restricted rotation, and 18/25 of the atoms in the chain are aromatic.

Part B The 15% solution of the polyimide in dimethylacetamide from Part A was filtered, degassed, and two films were cast on a Vydax coated glass plate at 100 C. with a 25-mil doctor knife. The films were covered and allowed to dry for 5 minutes at 100 C. The vents in the cover were then opened and drying was continued for 10 min utes. The films were stripped from the plate. One film was air-dried and used as a control. Another film was placed EXAMPLE 6 Part A.Polyimide from 3,4,3',4'-diphenylhexafiuoroisopropylidene tetracarboxylic dianhydride and p-phenylenediamine To a solution of 21.63 g. of p-phenylenediamine in 350 ml. of N,N-dimethylacetamide at 50 C. under nitrogen was added with stirring 88.87 g. of 3,4,3',4-diphenylhexafluoroisopropylidene tetracarboxylic dianhydride. Within minutes the temperature rose to a peak of 77 C. Stirring was continued for about one hour, at which time 82 g. of triethylamine and 82 g. of acetic anhydride were added. Stirring was continued for about 2 hours. The polyimide was precipitated by drowning the solution in a large excess of methanol under vigorous agitation. The polyimide was recovered by filtration, washed twice with methanol and dried under vacuum, first for 16 hours at room temperature and then for 3 hours at 260 C.

The polyimide prepared as shown above was checked against requirements (a), (b) and (c) as follows:

Restricted Rigid subunit Colinearlty N N N 20 Repeating unit has one L and 3 N subunits, 2 restricted bonds, all of the N subunits have at least one bond with restricted rotation, and of the atoms in the chain are aromatic.

Part B A solution of 45 g. of a polyimide like the one in Part A in 255 g. of dimethylacetamide was filtered through a 0.45;]. silver membrane, degassed, and two films were cast on Vydax coated glass plate at C. with a 25-mil doctor knife. The films were covered and dried for 5 minutes. The vents in the cover were then opened and drying continued for 10 minutes. The films were stripped from the plate. One film was air-dried and used as a control. Another film was placed in a vacuum chamber and heat-treated at 260 C. for 6 hours under a vacuum of Z The 1.3-mil control film permeated H at 3680 GTR and 2870 cB and CH at 66 GTR and 51 c3. The SHZ/CH4 was 56. The 1.2-mil heat-treated film permeated H at 5586 GTR and 4022 cB and CH at 29 GTR and 21 0B. The SEQ/CH4 was 193.

EXAMPLE 7 Part A.Polyimide from 3,4,3',4-diphenylhexafiuoroisopropylidcne tetracarboxylic dianhydride and the hisamide from m-phenylenediamine and m-aminobenzoic acid To a solution of 34.64 g. of N,N'-m-phenylenebis(maminobenzamide) in 175 ml. of dry N,N-dimethylacetamide under nitrogen at 50 C. was added with stirring 44.44 g. of 3,4,3',4'-diphenylhexafiuoroisopropylidene tetracarboxylic dianhydride, rinsed in with an added 25 ml. of dimethylacetamide. Within a few minutes the temperature peaked at 76.5 C. and began to drop. After stirring for about 1 hour, 41 g. of triethylamine and 41 g. of acetic anhydride were added. The temperature soon peaked at 66 C. and began to drop. After stirring for 2 hours, the polyimide was precipitated by drowning the solution in excess methanol under vigorous agitation. The polyimide was recovered by filtration, washed twice with methanol and dried under vacuum, first for about 18 hours at room temperature and then for 3 hours at 260 C.

The polyimide prepared as shown above was checked against requirements (a), (b) and (c) as follows:

Rigid subunit Restrlcted Colinearlty bonds 21 The repeating unit has 10 N subunits, two bonds with restricted rotation, three of the N subunits have at least one bond with restricted rotation, and 30/41 of the atoms in the chain are aromatic.

Part B A solution of 12 g. of the polyimide of Part A in 68 g. of dimethylacetamide was filtered through 0.45 1 silver membrane, degassed, and two films were cast on a Vydax coated glass plate at 100 C. with a 25-mil doctor knife. The films were covered and dried for 5 minutes. The vents in the cover were then opened and drying continued for minutes. The films were stripped from the plate. One film was air-dried and used as a control. Another film was heat-treated for 6 hours under a vacuum of 2 Heating was started at 100 C. and after 1 hour had reached 260 C. where it was held for the remainder of the treatment. The 1.62-mil control film permeated H1 at 1268 GTR and 1232 cB and CH at 24 GTR and 23 CE. The Sin/CH4 was 53. The 1.48-mil heat-treated film permeated H at 1360 GTR and 1208 cB and CI-L, at 1.5 GTR and 1.3 cB. The was 907.

EXAMPLE 8 Part A.-Polyimide from 3,4,3,4-diphenylhexafluoroisopropylidene tetracarboxylic dianhydride and 3,5-diaminobenzoic acid To a solution of 15.22 g. of 3,5 diaminobenzoic acid in 175 ml. of dry N,N-dimethylacetamide under nitrogen at 50 C. was added with stirring 44.44 g. of 3,4,3',4-diphenylhexafluoroisopropylidene tetracarboxylic dianhydride. rinsed in with an added 25 ml. of dimethylacetamide. Within 2 minutes the temperature peaked at 74.5 C. and began to drop. After about 1 hour of stirring,

82 g. of triethylamine and 82 g. of acetic anhydride were added. Within 14 minutes the temperature peaked at 56 C. and began to drop. After stirring for 2 hours the solution was concentrated to 25% polyimide in dimethylacetamide by evaporation under vacuum first at 50 C. and then at 100 C. It was then diluted to 10% polyimide by adding 332 g. of dimethylacetamide, followed by concentrating to 15% polyimide by evaporation and filtering through a 0.45 silver membrane.

The polyimide prepared as shown above was checked against requirements (a), (b) and (c) as follows:

A B C 4 5 2 0 E 5 /8 or, 5 it T or; N

C l, n OOH 5 0 Restricted Rigid subunit Colinearlty bonds N N C N C, D N D The repeating unit has 4 N subunits, 2 bonds with restricted rotation, 3 of the N subunits have at least one bond with restricted rotation, and 18/27 of the atoms in the chain are aromatic.

Part B To 20 g. of the polyimide solution from Part A was added 0.17 g. of ethylene glycol. The solution obtained was degassed and two films were cast on a Vydax coated glass plate at 100 C. with a -mil doctor knife. The

films were covered, dried for 5 minutes, after which the vents in the cover were opened and drying was continued for 10 minutes. The films were stripped from the plate. One film was air-dried and used as a control. The 1.31-mil control film permeated H at 2684 GTR and 2110 cB and CH at 29 GTR and 23 c8. The SHZ/QH4 was 93.

Part C The second film from Part B was heat-treated at 260 for 6 hours under vacuum of 2 During this heat treatment the pendant carboxyl groups in the diarnine reacted with ethylene glycol to form crosslinks. This was shown on a portion of the film which dissolved readily in dimethylacetamide before the heat treatment, whereas the heat-treated film was insoluble in dimethylacetaniide. The crosslinked polyimide of the heat-treated film was checked against requirements (a), (b) and (c) as follows:

A B C D A 2 a 0 i a 0 a l l s a g E i i g i i 5 f! i I I I i E o E 0 i g n u o 1 5 o 5 I i 2 I i C C A II Restricted Rigid subunit Collnearity ads 1 N A,B 2 N B, C 3 N C, D 4 N D, A

The crosslinked polyimide has 4 N subunits, 4 bonds with restricted rotation, all of the N subunits have at least one bond with restricted rotation, and 18/ 27 of the atoms in the main chain are aromatic. The clear, smooth, crisp, 1.38-mil crosslinked film are permeated H at 4732 GTR and 3918 cB and CH at 11 GTR and 9 cB. The SH2/CH4 was 430.

EXAMPLE 9 Part A.-Polyirnide from 3,4,3,4'-diphenylhexafiuoroisopropylidene tetracarboxylic dianhydride and 3,3-diaminobenzanilide To a solution of 15.05 g. of 3,3-diaminobenzanilide in ml. of N,N-dimethylacetamide under nitrogen at 50 C. was added with stirring 29.68 g. of 3,4,3',4'-diphenylhexafluoroisopropylidene tetracarboxylic dianhydride. Within a few minutes the temperature peaked at 55 C. After about an hour of stirring, 55 g. of triethylamine and 55 g. of acetic anhydride were added. After stirring for about an hour and a half the polyimide was precipitated by drowning in a large excess of methanol under vigorous agitation. The polyimide was recovered by filtration, washed twice with methanol and dried under vacuum, first for about 16 hours at room temperature and then for 3 hours at 260 C. At 0.1% concentration in dimethylacetamide at 25 C. the polyimide had an inherent viscosity of 1.15.

of the films with respect to hydrogen and methane. The results are shown in Table VII.

TABLE VII 26 acetamide and casting on a Vydax coated glass plate at 100 C. with a 25-mil doctor knife. The films were covered and dried at 100 C. for 5 minutes, after which the vents on the cover were opened and drying was continued Post t Thic" HPemeatim cmpermeam" 5 for 10 minutes. The films were then stripped from the tlme(hrs.) en GTR cB GIR cB H0011 plate. One of each pair of films was air-dried and used 2 72 5 353 8 735 38 61 m as a control. The other film was placed in a vacuum cham- 5:858 9:244 40 63 .6 her and heat-treated at 260 C. for 6 hours under a vac- 6-237 9-954 30 47 2 8 uum of 2 The films were then tested for permeation of 46 10.879 35 58 187 2 77 6 5 10 hydrogen and methane as shown in Table 1X.

TABLE IX H: CH4 Mole percent Thlckpermeation permeation Selecmess tivlty, Film 1, 5, ND ODA (mils) GT H B GTR cB H:/CH4

Control 100 0 2.71 3,542 5,759 144 235 25 Heat-treated. 100 0 2.77 6,060 10,072 30 60 168 ControL... 75 25 2.70 3,665 5,937 116 188 32 Heat-treate 75 25 3. 02 4, 502 8,158 32 58 141 ControL- 50 50 2.55 2, 754 4, 214 87 133 32 Heat-treat 50 5O 2. 74 4,344 7,142 33 54 132 o6ntro1 25 75 0. 95 6,566 3,743 129 73 '51 Heat-treated- 25 75 0.98 7, 493 4,406 43 25 174 Control 0 100 1.78 2, 455 2,625 45 4s 55 Heat-treated. o 100 2.07 2,837 3,524 16 20 177 Cast from 10% solution.

EXAMPLE 13 5 EXAMPLE 15 The film preparation of Example 2 was repeated and p A several films were used for testing the effect of the time of heat treatment at 260 C. on the permeation properties of the films with respect to hydrogen and methane. The results are shown in Table VIII.

TABLE VIII Thtek- Hz permeation CH4 permeation Se lec- Post treatment ness vity, time (hrs.) (mils) GTR cB GTR cB Hz/CH EXAMPLE 14 Part A A series of five polymers and copolymers were prepared, the first by repeating the procedure of Example 10, Part A. The second, third, fourth and fifth were prepared by the same procedure except that 25%, 50%, 75% and 100%, respectively, of the 1,5-diaminonaphthalene (1,5-ND) was replaced by a molecular equivalent amount of 4,4'-diaminodiphenyl ether (ODA).

Part B Two films were prepared from each of the five polyimides of Part A by preparing 20% solutions in dimethyland 88.5 mole percent (80 weight percent) of m-phenylenediamine, to obtain a copolyamide.

Part B Polyimide/polyamide blends were prepared by dissolving together in varying proportions (as shown in Table X) the polyimide of Example 1, Part A, and the polyamide of Example 15, Part A, above, the amounts of the two polymers being selected to give a total of 15% polymer weight in solution in dimethylacetamide. Two films of the resulting solutions were cast on Vydax coated glass at 100 C. using a 25-mil doctor knife. The films were first dried for 5 minutes at 100 C. with the cover vents closed and then for 10 minutes with the vents open. The films were then stripped from the plate. The first film was air-dried and used as a control. The second film of each pair was heat-treated at 260 C. for 6 hours under a hydrogen and methane as shown in Table X.

TABLE X Wt. percent H, CH

Thlckpermeation permeation Selec Poly- Polyness tivity' Film imide amide (mils) GT R cB GTR 0B HT/CH:

0 100 1. 42 248 211 l. 0 1. 0 248 0 100 1. 45 145 126 0. 3 0. 3 483 25 1. 52 961 876 14 13 69 75 25 1. 49 1, 277 1, 142 3 3 426 20 1. 38 1, 203 996 13 11 93 8O 20 1. 54 1, 181 1, 091 3 3 394 15 1. 39 l, 869 1, 559 58 48 32 85 15 1. 34 1, 975 1, 588 9 7 219 10 1. 28 1, 953 1, 500 35 27 56 90 10 1. 31 2, 555 2, 008 13 11 197 5 1. 46 2, 417 2, 117 56 49 43 95 5 1. 25 3, 885 2, 914. 27 20 144 0 1. 78 2, 458 2, 625 45 48 55 100 O 2. 07 2, 837 3, 524 16 20 177 27 EXAMPLE 15 Polyimide/polyamide blends were prepared by dissolving together in varying proportions the polyimide of Example 10, Part A, and the polyamide of Example 15, Part A. Amounts of the two polymers were selected to give a total of 15% polymer weight in solution in dimethylacetamide. Two films of the resulting solutions were cast on Vydax coated glass at 100 C. using a 25-mil doctor knife. The films were first dried for minutes at 100 C. with the cover vents closed and then for minutes with the vents open. The films were stripped from the plate. One film of each pair was air-dried and used as a control. The second film was heat-treated at 260 C. for 6 hours under a vacuum of 2,2. The films were then tested for perfilm permeated oxygen at 103 GTR and 88 cB and nitrogen at GTR and 13 cB. The S was 6.9.

EXAMPLE A solution of 15 g. of the polyimide of Example 5, Part A, and 4.5 g. of lithium nitrate in 85 g. of dimethylacetamide was filtered through a 0.45 1. silver membrane. Two films were cast from this solution on Vydax-coated Inconel plates at 100 C. using a -mil doctor knife. The films were covered and dried at 100 C. for 5 minutes. The cover vents were then opened and the films further dried at 100 C. for 10 minutes. The two films on their casting plates were then quenched into ice water where they were soaked for 15 minutes. The films were then meation of hydrogen and methane as shown in Table IX. stripped from the plates and soaked in fresh ice water TABLE xr Wt. percent H; CH1

Thickpermeation permeation S elec- Polyn twit amide (mils) GTR cB GTR cB 111/0 1 5o 59 1.39 1,413 1,178 43 29 59 1. 44 1, 310 1,132 4 a 323 25 1. 4a 2, 519 2, 419 100 s5 28 75 25 1. 44 3, 50s a, 290 23 20 155 so 20 1. 41 5, 122 2, 754 135 129 23 so 20 1.42 5,045 4,299 33 25 153 15 1. 38 3, 840 3, 180 139 115 28 Heat-treated s5 15 1.41 5,840 4, 941 41 34 142 Control 1o 1. 44 4,475 5, 851 195 15s 23 99 10 1.42 7,890 5,722 59 51 134 5 1. 41 5, 224 4, 508 212 187 25 95 5 1. 53 7,862 1,211 55 51 143 o 2.71 542 5,759 144 235 25 100 0 2.77 6,546 10,879 35 58 181 for minute Before the EXAMPLE 17 45 s testmg, first film was air-dried and the second film was heat-treated at 260 C. for 6 hours under a vacuum of 211.. The resulting films were asymmetric. The air-dried film permeated H, at 17,420 GTR and CH at GTR. The s was 112. The heat-treated film permeated H, at 20,499 GTR and CH at 181 GTR. The SHz/m was 113.

TABLE XII Thickness H CH1 (mils) permeation permeation 8:11:50-

y. Knits Film GTR eB GTR cB H4/CH.

3 0.23 16,258 2,244 126 129 3 0.27 17,730 2,872 184 96 10 0. 50 9, 952 2, 986 173 52 58 10 0.51 12,754 3, 49 15 260 25 1.61 3,054 2,950 70 68 44 Heat-treated 25 1. 27 4, 610 3, 513 14 11 329 EXAMPLE 18 EXAMPLE 21 The procedure of Example 6, Part B, was repeated except that the doctor knife thickness was varied in order to observe the effect of varying film thickness on the permeation of hydrogen and methane. Details of this study are shown in Table XIII.

Part A.--Polyester from isophthaloyl chloride and 2,2-b is- 3,5 -dichloro-4-hydroxyphenyl) propane A mixture of 183 g. of 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane, 1 liter of s-tetrachloroethane, 0.72 g. of

TABLE XIII Thickness H; CH4

(mils) permeation permeation ti8631;1 9-

Film Knife Film GTR 0B GTR cB Hl/CH Heat-treats 50 3. 33 3, 767 7, 526 18 35 209 EXAMPLE 19 70 AlCl and 101.6 g. of isophthaloyl chloride was heated The procedure of Example 9, Part B, was repeated to obtain a control film and a heat-treated film of the polyimide-amide. The 1.56-rnil control film permeated oxygen at 105 GTR and 98 cB and nitrogen at 23 GTR and and stirred under nitrogen at reflux for 1 hour. The resulting viscous polyester solution was allowed to cool and 1 ml. of water was added with vigorous stirring. The resulting solution contained about 17% polyester. The polyester was precipitated in hexane with vigorous agita- 22 cB. The $0 was 4.6. The 1.42-mil heat-treated 75 tion, filtered and dried.

30 The repeating unit of the polyester prepared as above viscosities in this and the following examples were measured at 0.1% weight/volume in dimethylacetamide at 25 C.

nd mm i a A d n a olthwo 6 m8 0 m E I nn S to et fib P .mm n E L 2 u W. Wu 0 0 4 m m D NNNNNN t w em H N 3 C C L i f \H 0a "m find C2 tm mm H mm 3 b B a. a W I m u. Wm m 1 m if: 1 t W A 123456 a o A so 0 a( 8 0 5 0 5 0 H l 3 3 4 4 5 one 7 f. nr t l S. m mmmmmmwwwm v8 do v G m 7 w w s memm m 6 m .W Am flmm mmfiOm ad uMB wamm ma dr m n DD A S t rinod II to n/ r W5 0 ofe an mmw m zmm wmc n& CH0 5 R W m d.w 5 M C flC E r n mmmm m o d N el u efi n O 4 W m flhmwfn mm. a m fimfl M dm m D d .1 e ma tle LNLNNNNN c m wn mas t 1 at a w p 2 B ea mummm m O t a nd t f fi ae 206.1 a w s C s h .lta a mwmwd cdsf n m m m nvmwo wm t w w wm w, m n o m t mm m o dfidmmk T H H we 3 nnaimw c|o|o 2 m amm u .tm M nw fe e d mmo m n m oemmmwa rm U n a n ,p d t R1 ar f O e m fl a N m .womc v w wfnaa l m m do VH 1 wmm mu m nm C11 m e 0 V acme;- d l S e 3r e mn m Mm le f fl nd a in A wv g em lllll J k O & avmm 0 cm m a U m was checked against requirements (a), (b) and (c) as follows:

1 bond with restricted rotation 2 of the N subunits have 1 bond with Part B A solution of g. of the polyamide from Part A in 160 g. of dimethylacetamide was filtered through a 0.4S silver membrane and degassed. Several films were cast on added in two portions with stirring and the resulting a Vydax-coated glass plate at 110 C. with a l5-mil Five of the films were each dried under a vacuum of 2 for 2 hours at C. and then beat- 55 The repeating unit has 6 N subunits,

restricted rotation, and 12/16 of the main chain atoms are aromatic.

doctor knife. The films were covered and dried for 5 minutes at C. with the cover vents closed and 10 minutes with the vents open. The films were stripped from control.

treated, respectively, at the temperatures shown in Table and 88 cB. The SIM/CH1L was 16. The 2.25-mil heat-treated film permeated H at 1528 GTR and 2063 c8 and CH at 11 GTR and 15 cB. The SHZ/CH4 was 139.

EXAMPLE 22 Part A.Poly(4-isopropyl-m-phenylene) isophthalamide A glass reactor equipped with a stirrer, reflux condenser and dropping funnels was flamed out under vacuum and purged with nitrogen. Into the reactor was placed 83.62 g. (0.567 mole) of 4-isopropyl-m-phenylenediamine (cumenediamine). Dimethylacetamide (884.2 g.) was solution was cooled to about 0 C. Isophthaloyl chloride (116.75 g., 0.575 mole) was added in small portions over a period of 6 hours, the reaction temperature being held in the range of 41 to 52 C. The reaction mixture was 70 the plate. The first film was air-dried only and used as a then drowned in ice and water with vigorous agitation. The precipitated polyamide was recovered by filtration and dried to constant weight. There was obtained g. 0t polyamide with inherent viscosity of 0.38. Inherent 75 XIV for 6 hours under a vacuum of 2 All the films were r 36 night at room temperature under a vacuum of 2 and then heat-treated at 260 C. for 6 hours under a vacuum of 2a. The 1.59-mil control film permeated H at 3641 GTR and 3474 c8 and CH at 226 GTR and 216 c8. The Sim/CH4 was 16. The 1.86-mil heat-treated film permeated H at 3524 GTR and 3933 cB and CH at 184 and CB. Th SHZ/CH4 Was 19.

EXAMPLE 28 Part A.Poly(2,5,2,5'-tetrachlorobiphenylene) isophthalamide Using a procedure like that of Example 22, Part A, a polyamide was prepared from 32.203 g. of 2,5,2',5'-tetrachlorobenzidine and 20.302 g. of isophthaloyl chloride 2 hours under a vacuum of 2;; and then heat-treated at in 170 1111- Of N-methylpyffolidone Solvent at 4 C- The recovered polyamide had an inherent viscosity of 0.81.

The repeating unit (I) has 6 N and 2 L subunits. The repeating unit (T) has 5 N and 3 L subunits. In both (I) and (T), one of the N subunits has 2 bonds with restricted rotation and 18/23 of the main chain atoms are aromatic.

Part B A solution of 15 g. of the copolyamide of Part A in g. of dimethylacetamide was filtered through a 0.8 1 silver membrane, degassed and two films were cast on a Vydax coated glass plate at 110 C. with a 15-mil doc- 10 tor knife. The films were covered, dried for 5 minutes at 110 C. with the cover vents closed and for 10 minutes with the vents open. The first film was air-dried and used as a control. The second film was dried at C. for

225 C. for 6 hours under a vacuum of 2;. The 1.43-mil air-dried film permeated H at 2304 GTR and 1977 cB mm A o md 0 0 7 %m G l d d mm a as on d 11 0., mm BBCD m F w pa R 0 0 5 MN... E IIIIII i mm w Wm 4 A I. m D m NLLNNNN 8 mm. 1 w 0 mm 1 3 I mm c m .m ma C I uuuuu I. m m m1 u 3 1 .w m .m C w ma m 2 o i e H w m 1 do one S llllllllllllll ll Cd m% A H mm Enema 0 5 0 5 M 2 2 3 3 I s 7 mm Maine 6 m owwinm a w M m w. m mw um tn o m wa n mw wm. 0 6 m NLNLNN 1 u um hmAmmm w ms F o m T .m ut mm Pm c a a mmw.mm mo e 5 2B m r. C m I ll. QmH m ym mvvmnme E n 9 2 ofi v r. .3 wu mamammmm. A m m m m an "MC 5. 00p 6 mm u 7 m m mwm w 4 an e t e 0 ac E 0 5 w. E e... emifiyma m a. m fim H mm m mmm mm D m 1 2 a 4 1 n .1 -00 C dfifl M eh 4 mm fd mdt m MwS Wf MOR HIICI 3 ea P e 3 ee 4 .8 R 4 m nsammvhm c Tm [.1 d t lnh om u m n um mm e i i I 1mm mum wmpmcm aw on 4ha k PSBYMW f l V. 7 l Oa d t 2 .lB A n dn wh ,C .e f EIO m M moomO S O 4 t 1f. 6 8 [P yuo I H4 a m 52 )B i C .16 P o h n 131 & mama mm wl\ HIN 1 106d Un am HT0d n n mh mhffim m aTaw tPtPoot s The repeating unit has 5 N and 2 L subunits and 3 bonds with restricted rotation. Two of the N subunits each have one bond with restricted rotation and 18/22 of the main chain atoms are aromatic.

Part B A solution of 15 g. of the polyamide of Part A in 85 g. of dimethylacetamide was filtered through a 0.45; silver membrane, degassed and two films were cast on a Vydax coated glass plate at C. with a 15-mil doctor knife. The films were covered, dried for 5 minutes with the cover vents closed and for 10 minutes with the vents open. The films were stripped from the plate and dried under a vacuum of 2; at room temperature overnight.

used as a control. The second film was first dried over- 75 The first film was used as a control. The second film was The repeating unit (I) has 6 N and 2 L subunits. The repeating unit (T) has 5 N and 3 L subunits. In both (I) and (T), three of the N subunits have at least 1 restricted bond and 18/23 of the main chain atoms are aromatic.

Part B A solution of 15 g. of the copolyamide of Part A in 60 g. of dimethylacetamide was filtered through a 0.8 4 silver membrane, degassed and two films were cast on a Vydax coated glass plate at 110 C. with a 15-mil doc- 70 tor knife. The films were covered, dried for 5 minutes at 110 C. with the cover vents closed and for 10 minutes with the vents open. The first film was dried overnight at room temperature under a vacuum of 2 and 38 under a vacuum of 2 and then heat-treated at 260 C. for 6 hours under a vacuum of 2p. The 1.48-mil control film permeated H at 609 GTR and 541 cB and CH at llGTR and 9.8 cB. The Sag/CH4 was 55. The 1.45-mil heat-treated film permeated H at 886 GTR and 771 0B and CH at 5.3 GTR and 4.6 CE. The was 167.

EXAMPLE 30 Part A.Poly(4,6-dichloro-m-phenylene)isophthalamide/terephthalamide In the manner of Example 29, Part A, a copolyamide was prepared from equimolar quantities of 4,6-dichloromphenylenediamine and a 70/30 mixture of isophthaloyl chloride/terephthaloyl chloride.

The repeating unit of the copolyamide noted above was checked against requirements (a), (b) and (c) as follows:

. h e A llll 1M 1' av 4m m n .m Hnw W 0 0 h 0 m n is. c F i I .m 6 k a .D mum u e wwm .1 a a1 m h d W L 4 M E ll 4 \l c s 1 .m T c n d u 2 O C m N n b 1 m BB a I. e 6 w m R 5. a a UN n {Fl-ll. 6 h .W 6 w D m OHJV m an I\ S f m m NNNN NL N .n N o r a n n ed. A W U 5 m we. Mm CL 9 m m mm 1 .l t llllllllllll ll f r S i 4 a \I) e U 3 m m m WM uh B ....l.... m m m e n m w s HIN s u u m m m llll kill! m n No.1 0 m k 1 u m i b a H l C 5 6 O O 6 2 a 4 G lllll llll in m C|D| mm BBCD Mb a 6 1 B w H N m .1 F m NLLNNLNLN 0 0 a w C 37 further dried for 2 hours at 100 C. under a vacuum of 2 and then heat-treated at 200 C. for 6 hours under a vacuum of 2 The 0.73-mil control film permeated H at 1315 GTR and 576 c8 and CH at 18 GTR and 8 C8. The Sin/CH4 was 73. The 0.76-mi1 heat-treated film permeated H at 1181 GTR and 539 0B and CH at 2.7 GTR and 1.2 CE. The SHMCH4 was 437. The heat-treated film permeated 0 at 36 GTR and 16 CE and N; at 5 GTR and 2.3 cB. The So2/N2 was 7.2.

EXAMPLE 29 Part A.Poly(2,5,2,5'-tetrachlorobiphenylene) oxydibenzamide Using a procedure like that of Example 22, Part A, a polyamide was prepared from 161.01 g. of 2,5,2',5-

tetrachlorobenzidine and 147.56 g. of the dichloride of Rigid subunit oxydibenzoic acid in 1200 ml. of dimethylacetamide solvent at 5-50 C. The recovered polyamide had an inherent viscosity of 0.76.

The repeating unit of the polyamide prepared as shown above was checked against requirements (a), (b) and (c) as follows:

Part B A solution of g. of the copolyamide of Part A in g. of dimethylacetamide was filtered through a 0.45 11. silver membrane, degassed and two films were cast on a G5 Vydax coated glass plate at C. using a 15-mil doctor knife. The films were covered, dried for 5 minutes at 90 C. with the cover vents closed and for 10 minutes with the vents open. The first film was air-dried and used as a control. The second film was air-dried and then beatdried for 5 minutes 7 treated at 260 C. for 6 hours under a vacuum of 211.. The 1.17-mil control film permeated H at 574 GTR and 403 0B and CH at 7.4 GTR and 5.2 cB. The Slag/CH4 was 78. The 1.16-mil heat-treated film permeated H at 499 GTR and 347 c8 and CH at 1.3 GTR and 0.9 cB. The 832mm 7 was 384.

Part B A solution of 15 g. of the polyamide of Part A in 85 g. of dimethylacetamide was filtered through a 0.45;. silver membrane, degassed and two films were cast on a The repeating unit has 5 N and 4 L subunits and 3 bonds with restricted rotation. Two of the N subunits each have one bond with restricted rotation and 24/29 of the main chain atoms are aromatic.

Vydax coated glass plate at 110 C. with a 25-rnil doctor knife. The films were covered,

at 110 C. with the cover vents closed and for 10 minutes with the vents open. The films were stripped from the plate and dried under a vacuum of 2 at room temperature overnight. The first film was used as a control. The second film was further dried for 2 hours at C. 

